1. Technical Field
This invention relates to a method and apparatus for producing solid parts by exploiting differences in material properties between two material classes with distinctly different behavioral characteristics at certain thermal, mechanical, and chemical environmental conditions. In particular, this invention relates to a controlled material handling and processing apparatus which deposits a plurality of materials to form a spatially controlled material composition powder mass which may be subsequently subjected to appropriate thermal, mechanical, and chemical environmental conditions to unify one material class into a three dimensional part. The material(s) of the other class will remain separated and able to be removed, or alternatively, the other material(s) will be unified but distinctly separate from the first material class and, subsequently removable, thus freeing the three dimensional solid part.
2. Description of Relevant Art
The advancements of Computer-Aided Design (CAD) systems and computer graphics technology have provided for significant increases in design capability. Designs can be modeled and visualized in three dimensions, and in some cases simulations of physical phenomena can be performed. There are times, however, when a computer generated image cannot serve as an adequate substitute for a physical part. Employing conventional manufacturing processes to manufacture such parts is often time consuming and costly. When relatively small quantities of a given part are required and a conventional manufacturing process is used, material removal processes such as milling, drilling, grinding, and lathe cutting are most often used. These subtractive processes involve removing material from an initial piece of stock material. These processes may require the following: multiple tool changes, tool path planning, fixturing and subsequent re-fixturing, and significant operator intervention. These factors increase the time and cost of producing a part, and slow the product design and evaluation cycle.
Rapid Prototyping is commonly known as a broad class of specific processes which can produce a small quantity of physical parts in a relatively short time. Rapid Prototyping processes can produce physical parts which accurately represent "final part" geometry. As is known in the art, there is a difference between a form part, which essentially models the shape of the "final part" while providing only minimal structural strength, and a functional part which models the shape of the "final part", provides structural strength and accurately represents the desired properties of the "final part". The majority of existing Rapid Prototyping processes produce only form prototypes. When structural strength comparable to that achieved by conventional manufacturing processes is required, a secondary manufacturing process, in addition to a Rapid Prototyping process, is usually used to create a functional part. Most existing Rapid Prototyping processes are limited, either by the materials on which they can operate, by their accuracies or by the part geometries which they can produce.
A particular class of Rapid Prototyping technologies has developed significantly in recent years and is termed Solid Freeform Fabrication ("SFF"). SFF processes are primarily material addition processes where parts are fabricated via the additive composition of raw material rather than the subtractive material removal operations (which begin with an initial material block). SFF processes are typically driven by computer solid model information and tend to minimize human intervention required between the design of a part and its physical realization using such a system. Benefits of such approaches include minimizing material waste, low per-part setup cost, independence from part specific hard tooling, and no cutter path planning. Moreover, many SFF processes do not require fixtures or manual part re-positioning during part production. In some cases, it is possible to integrate assembly of multiple parts by fabricating them in their final assembled configuration. Using SFF, complex part geometries, some unrealizable from conventional manufacturing processes, can be produced. Most existing SFF processes can only be used for the production of form prototypes, disposable tooling, and patterns for secondary manufacturing processes such as investment casting.
There are other manufacturing processes which utilize material additive techniques. Welding, plasma spray, and plating are examples; however, these processes create parts given some initial geometry defining material substrate. Moreover, recently developed Solid Freeform Fabrication processes are capable of creating parts in a layer-wise fashion without requiring an initial geometry defining substrate. Examples of such fabrication processes are disclosed in U.S. Pat. Nos. 4,575,330; 4,752,353; and 4,863,538. These recent uses of layer-wise additive manufacturing techniques have been largely limited to producing form parts which are of relatively weak physical strength and/or parts with homogeneous material properties. Furthermore, many processes are limited to producing parts composed of specific polymer materials because of the solidification mechanism employed. For example, Stereolithography and Solid Ground Curing which rely on light induced chemical reactions to form solid material, are limited to operate on photo-polymer resins.
It is therefore desirable to utilize an additive material manufacturing process which may be used to produce functional parts in single quantities and small lot sizes.
It is also desirable to utilize a technique which places minimal restriction on the variety of materials which can be processed.
It is also desirable to utilize an additive manufacturing technique which is capable of creating parts with spatially controlled material compositions therein.
It is also desirable to achieve an apparatus for performing the aforementioned part manufacturing process which may be driven by a computer utilizing solid model information.